blendoor motor actuator, easiest way to tell is to first turn it to heat and let it sit for several minutes then switch it to a.c, if no change then its the actuator, if there is a change check the heater core

i think what he's saying is to see if there is a difference between all the way cold (blue) and all the way hot (red) - if there is then you know that the blend doors are working and you most likely need a new heater core.

thermostat does nothing for the ac/heating system, im willing to bet its the actuaor for the blendoor, another way to tell is have the speed **** on low and the car on the acc position not on, and switch it from max cool to to max heat, you should hear a slight wine from the actuator

thermostat does nothing for the ac/heating system, im willing to bet its the actuaor for the blendoor, another way to tell is have the speed **** on low and the car on the acc position not on, and switch it from max cool to to max heat, you should hear a slight wine from the actuator

That statement is wrong if your thermostat is stuck open the truck will never see operating temps